missing simple algebraic math concept for solving a formula (digital FIR filters)

Status
Not open for further replies.

robismyname

Full Member level 6
Joined
Jan 17, 2008
Messages
390
Helped
11
Reputation
22
Reaction score
9
Trophy points
1,298
Location
Central Florida
Activity points
4,603
General math concepts slips my mind for solving for a variable called "δ1" in the following example (Example 7.1-below)

EXAMPLE 7.1

In a certain filter’s specifications the passband ripple is 0.25 dB, and the stopband
attenuation is 50 dB. Determine δ1.

Answer says:

Using ( formula 7.1)

Rp = −20 log10 * [(1 − δ1)/(1 + δ1)]> 0 (≈ 0) [Formula 7.1]

we obtain

Rp = 0.25 = −20 log10*[(1 − δ1)/(1 + δ1)]⇒ δ1 = 0.0144


The author left out a few steps that i cannot seem to remember to execute from previous algebra experience. Does any one care to relieve me of some of my ignorance? Specifically how do you solve for "δ1" when its located in te num and den?

I attached the full page from the book for added convenience.

 

The formula is: Rp=-20*Log[(1-δ)/(1+δ)]

then: -Rp/20 = Log[(1-δ)/(1+δ)] from which:

10^(-Rp/20) = (1-δ)/(1+δ) ==> 10^(-Rp/20) + δ•10^(-Rp/20) = 1-δ thus:

δ•[1+10^(-Rp/20)] = 1-10^(-Rp/20) solving by δ:

δ = [1-10^(-Rp/20)]/[1+10^(-Rp/20)]
 

Status
Not open for further replies.

Similar threads

Cookies are required to use this site. You must accept them to continue using the site. Learn more…